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The back pressure rise in a supersonic air intake could affect the engine performance and, in extreme conditions, result in a catastrophic unstart phenomenon. The present study compares different back pressure states that occur during an unstart of a mixed-compression air intake at Mach 3 using a fast-response pressure-sensitive paint, with an emphasis on the isolator flow. At low back pressure, the isolator dynamics is strongly correlated with the unsteadiness around the external compression corner. At high back pressure, a normal shock train dictates the isolator flowfield from its leading shock foot downstream. At the onset of unstart, an oblique shock train transpires involving large-scale flow separation, boundary layer thickening, and mitigated unsteadiness at the isolator floor. Like in previous studies, the prominence of low-frequency unsteadiness and upstream wave propagation is observed at high back pressure. However, in addition, the present study shows strong upstream communication of back pressure in a narrow frequency band through acoustic mechanisms, that eventually leads to the intake unstart. At the onset of unstart, the prominent frequency varies linearly along the isolator length, matching closely with the half-wave resonator model. Suppressing the oscillations at the preferred frequencies could be a promising control strategy to mitigate or delay intake unstart. When the intake unstarts, a 3D bifurcated shock stands at the inlet and the unsteady flow spillage takes place around oblique shocks off the sidewalls at low frequencies.

Gas turbines are used in various industries, including aviation, oil and gas, transportation, and power plants to generate electricity. One of the critical issues in the operation of gas turbines in cold weather is to prevent ice formation at the inlet guide vanes and bell-mouth of the compressor. Among the various anti-icing methods, the use of hot air extraction from the compressor is preferred due to its straightforward design, low maintenance costs, and high efficiency. In the present paper, a numerical study is performed on using the anti-icing system by hot air extracted from the compressor for the Nowshahr 460 MW combined cycle power plant. The effects of hot air flow rate, number of anti-icing tubes, number of nozzles, and injection angles on the ice formation are investigated. The predicted results and experimental data are in good agreement. The results show that the outlet temperature from the air intake and temperature of filter surfaces increases favorably by using an anti-icing system. Also, the increase in the hot air flow rate, the number of injection nozzles and the anti-icing tubes decrease the possibility of ice formation on the filter surfaces. At the inlet temperature of −5 °C, by increasing the number of nozzles from six to ten, the average surface temperature of the filters increases by 2 °C, and the outlet temperature of the air intake increases by 152%. Ice formation is significantly reduced when two anti-icing tubes are used instead of one with an identical hot air flow rate.

Hydrocarbon traps in the air intake system (AIS) are a common method for controlling evaporative emissions from the air intake path. Several different systems are available, but there is no standard method for determining their efficiencies. Therefore, a component test rig for hydrocarbon traps was developed. Some optimizations were necessary to achieve emission characteristics observed in engine measurements. Using this setup, several measurements were performed on four different hydrocarbon traps. The results were in reasonable agreement with those from engine measurements. Two different hydrocarbon (HC) traps were selected for further studies. In these studies, the repeatability and the dependency of the emission mass level were investigated. Furthermore, the hydrocarbon concentration in the air filter box was determined using point source flame ionization detector (FID) sampling and a metal oxide semiconductor (MOS) sensor. The data showed a correlation with the emission mass determined in a sealed housing emission determination (SHED) test.

Air intakes are critical components in maximizing the efficiency of jet-powered engines. Their diverse designs, ranging from conventional shapes to innovative configurations, coupled with the intricate interplay of fluid dynamics, boundary layer effects, and structural considerations, render the determination of their performance characteristics a time-consuming task. However, a meticulous and confident evaluation of these characteristics is the key to achieving optimal air intake design and, consequently, significant enhancement of overall engine performance. This article assesses various meta-modeling approaches for predicting the performance characteristics of a twin air intake system. A comprehensive exploration of meta-modeling methods, particularly those specifically tailored for data derived from experiments, is presented. A database of 4000 experimentally obtained runs is utilized to construct train and test data for diverse models, including polynomials, decision trees, random forest regression, multivariate adaptive regression splines, and neural networks. The performance of each model is rigorously evaluated based on goodness of fit, precision, accuracy, monotonicity, and interpretability. This study provides a cost-effective and time-efficient alternative for predicting crucial flow parameters associated with the air intake of jet engines. The results reveal that the Random Forest Regression (RFR) model outperforms all other models across all evaluated metrics, demonstrating its superior effectiveness in predicting the performance characteristics of the twin air intake system.

In order to avoid radar detection of the aircraft engine in a combat aircraft, serpentine duct is used in the air intake system. Due to change in geometry, the core flow path undergoes change in direction resulting in secondary flows and possible separation. The main requirements of a combat aircraft air intake is to deliver design airflow to the engine with minimal distortion and pressure loss. While flow distortion can increase the chances of engine stalling, large pressure loss will adversely affect engine overall performance. To address these requirements, both active and passive flow control techniques have been used in practice. Mechanical vortex generator is one of the passive flow control technique and it is attractive due to lesser complexity and the cost involvement. The formation of vortex and its interaction with the core flow is to be carefully analysed to have better design. Co-flow and counter flow vortex generators are reported in the literature. In the present work, effect of co-flow vortex generator on the flow field in an elliptic to circular cross section serpentine duct has been considered. The curvature of the bends is high, and the flow in the lower surface of the first bend interacts with upper surface of the second band in the mid-plane. The vortex generators are placed at the lower surface of the first bend and also at the upper surface of the second bend.The flow field created by the vortex generators placed at the lower surface of the first bend interacts slightly more with the upper surface of the second bend than the baseline case due to slight reduction in separation length. It alters the internal pressure field and improves flow uniformity. In the case of placement of vortex generator at the upper surface of the second bend alone did not show any significant variation on flow uniformity. Vortex generator placed at the lower surface of the first bend and the upper surface of the second bend helps to achieve better flow uniformity except at the upper portion of the aerodynamic inlet plane of the engine. The flow uniformity is improved with reduction in DC-60 by 11% and the pressure recovery is reduced by 6% as compared to the base design without the vortex generators. The trade-off between flow uniformity and pressure recovery clearly indicates placing of vortex generator at the lower surface of first bend is better for this serpentine duct having 2.6% reduction in pressure recovery and improvement in flow uniformity having 9% reduction in DC-60 as compared with baseline duct.

In the industrial environments, one of the ways to prevent the spread of harmful fire by-products to adjacent compartments via ventilation networks consists in applying an Inlet Valve Closure procedure. A theoretical research by means of the experiments and the physics-based models is performed to investigate the consequences of closing air intake on fire behavior in the mechanically ventilated compartment. In well-ventilated conditions, the strategy of closing inlet vent can be considered as a positive factor with a reduction in HRR regardless of fuel type such as heptane or dodecane. In under-ventilated conditions, replacing heptane by dodecane with a higher boiling point leads to a change in fire dynamics regime from a ventilation to fuel controlled fire. Closing inlet vent contributes to a faster heptane fire growth with an increase in theoretical HRR by a factor of 5%, and however, exhaust of the ventilation controlled fire occurs more easily due to a reduction in combustion efficiency by a factor of 30%. However, for the dodecane fire, closing inlet vent facilitates a reduction in HRR over a longer burning period. Air entering the compartment follows closely the fluctuations of the fire induced pressure as a result of strong coupling process between drop in pressure and inlet flow rate. For the heptane fire in vitiated air environment, the impact of stopping inlet vent on the peak of unburnt species concentration seems negligible. Dodecane with a longer carbon chain produces more unburnt gases than heptane, and turning off air intake results in a reduction in unburnt species. Occurrence of flame extinction in the vitiated air enclosure makes a sudden supply of fresh air from dilution duct with an oxygen concentration of about 15%, ideal condition for triggering an eventual auto-ignition of a fuel–air mixture. With regarding the delay time for an ignition risk of unburnt pyrolyzates, the heptane fire appears more dangerous by closing inlet vent. For the dodecane fire, stopping inlet vent contributes to a prolongation in ignition delay time of unburnt pyrolyzates.

Serpentine air intake system is an essential requirement in modern combat aircraft. Flow control techniques are used to achieve the desired performance of flow uniformity and pressure recovery. Mechanical vane type vortex generator designed in the previous work is considered as a flow control technique. The performance of vortex generator at various off-design conditions of different subsonic throat Mach numbers and three different altitudes are of interest to this present study. Numerical simulations were performed for throat Mach numbers from 0.45 to 0.7 in the increment of 0.05, with and without vortex generator at sea level static inflow condition. Flow non-uniformity and pressure losses were found to increase with increase in Mach number. However, flow uniformity is better with vortex generators for all Mach numbers with slight reduction in total pressure recovery at sea level condition. In order to check the effect of increasing altitude, duct with VG was simulated for 6 km and 11 km altitudes. All the simulations are conducted with reducing the inlet total pressure from sea level to represent the altitude and varying the exit static pressure to arrive at the desired throat Mach number. In general, Reynolds number decreases with increasing altitudes and promotes the possibility of flow separation. While reduced pressure recovery was seen, DC-60 was lower at 6 km altitude for all the Mach numbers. Higher value of DC-60 at sea level condition is primarily due to the dynamic pressure at AIP. Generally, a threshold value of DC-60 is to be given as a design requirement. Present design of vortex generator has reduced DC-60 value from 29.7 to 20.7 at 0.65 Mach number and sea level condition with a maximum of 25 from all the other conditions, thereby proving its benefits.

Based on the literature data, various factors of different natures influence the strength characteristics of high-temperature composite materials, and the performance of aerospace engineering structural elements under operating conditions is analyzed. The general approaches to modeling the operating conditions of structural elements on gas-dynamic benches are presented. The study used approaches to model the external impact on the structural element and equivalence of material damage processes in model and full-scale conditions. These approaches are based on the classical theories of similarity and dimensionality, the main provisions of which have been transformed and adapted to the problems of studying the strength of composite materials and the kinetics of damage to structural elements made of them in high-temperature gas flows. The methodology’s basic principles and the corresponding methods for studying their performance have been implemented for structural elements as the edges of direct-flow jet engines’ air intakes. As the basic equipment, a test complex of gas-dynamic test benches was used, the design features of which and methodological solutions provide a full cycle of bench tests to solve the tasks. Based on the experimental and analytical generalization of the boundary conditions of heat transfer in bench conditions, numerical modeling of the dependence of the thermal stress state of the models on the geometric parameters and thermal and physical characteristics of the studied materials was performed. It is shown that such comparative tests with several materials should be carried out on models of the same shape and geometric dimensions since the difference significantly affects structural elements’ stress state.

Results of a numerical simulation of an unsteady flow in an axisymmetric intake with internal compression tested in a hotshot wind tunnel with a fixed-volume settling chamber are discussed. The present simulations reveal the main features of various modes: unsteady processes of wind tunnel and intake starting, quasi-steady flow over the started intake with a supersonic flow velocity in the intake duct, and subsequent ulterior transition to the flow with a detached bow shock wave in front of the air intake with a subsonic flow velocity in the duct. A previously unknown mode of the flow over the intake with oscillating motion of the bow shock wave is observed. It is shown that oscillations decay with time, and the bow shock wave position in the incoming flow becomes stabilized at a certain distance from the leading edge of the intake with the test flow in the wind tunnel being preserved.

In this study, the pressure loss value of air intake hose of FIAT 1.3 E6D type engine, located between intercooler and inlet manifold of the engine, was examined using computational fluid dynamics, considering geometrical deformation in a rubber material. The rubber material modelling was performed by the verification of the data - obtained through the experimental method- with ANSYS software using Mooney-Rivlin method. The rubber material modelling was performed with the aim of correctly determination of the increase in the hose diameter when subjected to pressure, since the material has the feature of elasticity. In this study, ANSYS Fluent v.18.0 software and a static pressure machine were used. The air intake into the hose took place at the pressure of 123,5 kPa and flow rate of 0,087 kg/s. A solution, independent of the number of element, was obtained in the analysis. The turbulence model used in the study is standard k-ε type. As a result, the deformation-oriented pressure loss in the last geometry was found 1,85 kPa. The analyses were repeated for non-deformed geometry, and a pressure loss of 2,04 kPa was determined. At the result of the test, the geometry was seen to become actually deformed, and the pressure loss was found 1,9 kPa. The lowness of pressure loss in the deformed geometry was seen as the removal of the sharp bends that would cause local losses with the effect of pressure forces. In this study, it was determined that geometrical deformation changes the geometrical features that causes pressure loss, and leads to less pressure loss.